1. Field of the Invention
The present invention relates to an improvement of an electronic key apparatus for vehicle, which verifies ID codes through communications between portable devices and on-vehicle devices, for locking or unlocking of doors, a steering wheel, and a trunk of the vehicle, starting an engine, or the like.
2. Description of the Related Art
Up to now, there is an electronic key apparatus with which, to lock or unlock doors of a vehicle or start an engine of the vehicle, a user inserts a key into a keyhole and turns the key. Further, there is another key apparatus with which, like a so-called card key, while a key is kept in a pocket or bag of a user of a vehicle, wireless communication is established between an on-vehicle device and the key (portable device) without the key being touched, and an ID code sent from the portable device is compared with an ID code stored in the on-vehicle device. In this key apparatus, if the ID codes match, the on-vehicle device unlocks or locks the doors of the vehicle only by touching a sensor mounted to a doorknob (for example, see JP 2000-54699 A and JP 2006-108981 A).
Further, in the above-mentioned electronic key apparatuses, the on-vehicle device periodically transmits a radio signal for making a request to perform verification. When a portable device registered in advance approaches a vicinal area from which the vehicle can be unlocked, the portable device responds to the radio signal and the on-vehicle device verifies the response signal sent from the portable device (for example, see JP 2000-54699 A).
In the above-mentioned JP 2000-54699 A, in order to improve responsiveness for locking/unlocking doors of a vehicle through the communication between the portable device and the on-vehicle device, the on-vehicle device improves the responsiveness while improving a power saving property by changing a transmission period according to a reception strength.
Further, in JP 2006-108981 A, through the communication between the portable device and the on-vehicle device, it is judged whether a noise is generated based on the reception strength in order to store causes for an abnormal control and operation of the locking/unlocking of the doors.
However, in a case where the signal is destroyed due to interference of radio waves which have been simultaneously transmitted or generation of a noise, ID verification according to the signal cannot be performed. Accordingly, there has been a possibility that the locking/unlocking of the doors is delayed until subsequent verification is made or the locking/unlocking of the door is not operated.